Influence of Alkali Treatment on the Mechanical Properties of COIR Fiber Polymer Composites

Abstract

This study presents the design, fabrication, and characterization of sustainable coir fiber–reinforced polymer composites based on cashew nut shell liquid (CNSL)–modified epoxy resin, with potential relevance to tribological and structural applications. Three composite configurations—interlocked untreated coir fibers, randomly oriented untreated fibers, and NaOH-treated coir fibers—were manufactured using the vacuum bagging technique with an epoxy-to-hardener ratio of 1:1.25 and CNSL content ranging from 15 to 20 wt.%. The composites were evaluated through tensile, flexural, and impact testing to assess their mechanical performance, while Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were employed to analyze chemical structure, thermal stability, and fracture morphology, respectively. The results indicate that interlocked coir fiber composites exhibit superior mechanical strength and structural integrity compared to randomly oriented systems, attributed to improved load transfer and fiber interlocking. The incorporation of CNSL enhanced impact resistance and thermal stability, which are critical for durability under service conditions involving repeated loading and surface interactions. However, excessive NaOH treatment was found to reduce impact toughness due to fiber degradation. The outcomes highlight the potential of CNSL-modified coir fiber composites as eco-friendly materials for tribology-related components in automotive, construction, and light engineering applications. Future research should focus on optimizing fiber surface treatments, fiber loading, and wear behavior to further enhance tribological performance.